Besides the slicer, if you want a more accurate single wall, it needs to match that which the nozzle prints.. For instance a .4mm nozzle can much more accurately print a wall that is .45mm in width. When plastic is extruded it expands and is larger than the hole it came out of. Slices can try and compensate for this but I have personally found the results are better if you go .2-.4 larger than the nozzle. The model should be made to match that of the extrusion width if at all possible.